Zirconium alloy composition having excellent corrosion resistance for nuclear applications and method of preparing the same

ABSTRACT

The present invention relates to a zirconium alloy composition having excellent corrosion resistance for nuclear applications and a method of preparing the same. The zirconium alloy composition having excellent corrosion resistance for nuclear applications includes 1.3˜2.0 wt % of niobium, 0.05˜0.18 wt % of iron, 0.008˜0.012 wt % of silicon, 0.008˜0.012 wt % of carbon, and 0.1˜0.16 wt % of oxygen, with the balance being zirconium, or includes 2.8˜3.5 wt % of niobium, 0.2˜0.7 wt % of at least one of iron and copper, 0.008˜0.012 wt % of silicon, 0.008˜-0.012 wt % of carbon, and 0.1˜0.16 wt % of oxygen, with the balance being zirconium. The zirconium alloy composition according to the present invention, in which the amount of niobium, acting as a first alloying element, and the amount of at least one of iron and copper, acting as a second alloying element, are appropriately controlled, and silicon, carbon and oxygen are added in appropriate amounts, can exhibit excellent corrosion resistance, and thus can be usefully used as materials for nuclear fuel cladding tubes, support ribs, and core components of light water reactors and heavy water reactors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zirconium alloy composition havingexcellent corrosion resistance for nuclear applications and to a methodof preparing the same.

2. Description of the Related Art

During the last several decades, zirconium alloys, which have a smallneutron absorption cross section and excellent corrosion resistance andmechanical properties, have been widely used as materials for nuclearfuel cladding tubes, nuclear fuel assembly support grids, and structuralcomponents in pressurized water reactors (PWRs) and boiling waterreactors (BWRs). Among zirconium alloys developed to date, particularlyuseful are Zircaloy-2 (1.20˜1.70 wt % of tin, 0.07˜0.20 wt % of iron,0.05˜1.15 wt % of chromium, 0.03˜0.08 wt % of nickel, 900˜1500 ppm ofoxygen, and the balance being zirconium) and Zircaloy-4 (1.20˜1.70 wt %of tin, 0.18˜0.24 wt % of iron, 0.07˜1.13 wt % of chromium, 900˜1500 ppmof oxygen, less than 0.007 wt % of nickel, and the balance ofzirconium), comprising tin (Sn), iron (Fe), chromium (Cr) and nickel(Ni).

However, in recent years, as part of the economic improvement of nuclearreactors, in order to decrease nuclear fuel cycle costs, high burn-upoperation due to an extended refueling cycle has been adopted.Accordingly, as the refueling cycle is extended, the duration ofreaction of the nuclear fuel with high-temperature and high-pressurewater and steam is increased. Thus, in the case where conventionalZircaloy-2 or Zircaloy-4 is used as material for nuclear fuel claddingtubes, problems in which the nuclear fuel is severely corroded are onthe rise.

Hence, there is an urgent need for the development of high burn-upnuclear fuel cladding material having superior corrosion resistance withrespect to high-temperature and high-pressure water and steam. A lot ofresearch is being directed toward the development of zirconium alloyshaving improved corrosion resistance. As such, since the corrosionresistance of the zirconium alloy is greatly affected by the types andamounts of elements to be added, the working conditions, and heattreatment conditions, establishing optimal conditions is the mostimportant factor for the induction of excellent corrosion resistance.

When briefly investigating patents concerning cladding tubes of highburn-up and extended cycle nuclear fuel, registered after the middle ofthe 1980s, the addition of niobium (Nb) and the decrease in the amountof tin (Sn) are characteristic, compared to the Zircaloy-based alloys.That is, the zirconium alloy for high burn-up and extended cycle nuclearfuel essentially contains niobium, and the optimal preparation processthereof is provided to exhibit excellent performance. Further, for highcreep resistance, zirconium alloys, in which a small amount of sulfur(S) is added, are registered, and high corrosion resistance accompaniesthe control of amounts of alloying elements.

U.S. Pat. No. 4,649,023 discloses a zirconium alloy, comprising 0.5˜2.0wt % of niobium, 0.9˜1.5 wt % of tin, 0.09˜0.11 wt % of one elementselected from the group consisting of iron, chromium, molybdenum,vanadium, copper, nickel, and tungsten, and 0.1˜0.16 wt % of oxygen,with the balance being zirconium, and also a process of preparing thealloy, in which the size of the precipitate in a matrix is limited to 80nm or less.

U.S. Pat. No. 5,112,573, which specifies the alloy composition disclosedin U.S. Pat. No. 4,649,023, discloses a process of preparing a zirconiumalloy, comprising 0.5˜2.0 wt % of niobium, 0.7˜1.5 wt % of tin,0.07˜0.14 wt % of iron, 0.03˜0.14 wt % of nickel or chromium, and 0.022wt % or less of carbon, with the balance being zirconium.

U.S. Pat. Nos. 5,125,985 and 5,266,131 disclose a process of preparing azirconium alloy having the same composition as that disclosed in U.S.Pat. No. 5,112,573, in which a β-quenching process is introduced at alate stage during cold-rolling of the above alloy, in order to increasecreep resistance and corrosion resistance.

U.S. Pat. No. 5,648,995 discloses a method of preparing a zirconiumalloy comprising 0.8˜1.3 wt % of niobium, 0.005˜0.025 wt % of iron, 0.16wt % or less of oxygen, 0.02 wt % or less of carbon, and 0.012 wt % orless of silicon, with the balance being zirconium, in which the amountof iron is controlled to be very low so as to increase creep resistance.

U.S. Pat. No. 5,832,050 discloses a method of adding 8˜100 ppm of sulfurto eight various zirconium alloys, including a zirconium alloy composedof 0.7˜1.3 wt % of niobium, 0.09˜0.16 wt % of oxygen and the balance ofzirconium, in order to increase creep resistance, and a process ofpreparing these alloys.

U.S. Pat. No. 6,544,361 discloses a zirconium alloy comprising 0.8˜1.3wt % of niobium, 0.05˜0.2 wt % of oxygen, 300 ppm or less of tin, 0.25wt % or less of iron+chromium+vanadium, and 5˜35 ppm of sulfur, and aprocess of preparing material for a thin strap having excellentresistance to creep, corrosion, and hydrogen absorption.

U.S. Pat. No. 5,940,464 discloses an alloy composition, comprising0.8˜1.8 wt % of niobium, 0.2˜0.6 wt % of tin, 0.02˜0.4 wt % of iron,30˜180 ppm of carbon, 10˜120 ppm of silicon, and 600˜1800 ppm of oxygen,with the balance being zirconium, and a preparation process thereof, inorder to increase corrosion resistance and creep resistance.

U.S. Pat. Nos. 6,261,516, 6,514,360 and 6,902,634 disclose variouszirconium alloy compositions, including a zirconium alloy composed of1.1˜1.7 wt % of niobium, 600˜1600 ppm of oxygen and 80˜120 ppm ofsilicon, and a preparation process thereof. As such, the preparation ofthe zirconium alloy, having excellent corrosion resistance, requiresthat heat treatment temperature and time, the precipitate size, and theconcentration of niobium oversaturated in a matrix be controlled.

In U.S. Pat. No. 4,938,920, the amount of tin is decreased to 0˜0.8 wt%, and 0˜0.3 wt % of vanadium, 0˜1.0 wt % of niobium, and 1000˜1600 ppmof oxygen are added to develop an alloy having higher corrosionresistance than that of conventional Zircaloy-4. In this case, theamounts of iron and chromium are set in the range of 0.2˜0.8 wt % and0˜0.4 wt %, respectively, and the sum of iron, chromium and vanadium islimited to 0.25˜1.0 wt %.

U.S. Pat. No. 5,254,308 discloses a zirconium alloy containing niobiumand iron, which function to prevent the deterioration of the mechanicalproperties of the alloy, attributable to a decrease in the amount oftin, to improve the corrosion resistance of the alloy. This alloy iscomposed of 0.45˜0.75 wt % of tin, 0.4˜0.53 wt % of iron, 0.2˜0.3 wt %of chromium, 0.3˜0.5 wt % of niobium, 0.012˜0.3 wt % of nickel, 50˜200ppm of silicon, and 1000˜2000 ppm of oxygen. The ratio of iron tochromium, which may affect the corrosion properties, is fixed at 1.5,and the amount of niobium is determined depending on the hydrogenabsorption. Furthermore, the amounts of nickel, silicon, carbon anddissolved oxygen are finely controlled, resulting in excellent corrosionresistance and strength.

U.S. Pat. No. 5,334,345 discloses an alloy composition, comprising1.0˜2.0 wt % of tin, 0.07˜0.7 wt % of iron, 0.05˜0.15 wt % of chromium,0.16˜0.4 wt % of nickel, 0.015˜0.3 wt % of niobium, 20˜500 ppm ofsilicon and 900˜1600 ppm of oxygen, in order to increase corrosionresistance and hydrogen absorption.

U.S. Pat. No. 5,366,690 discloses an alloy composition, in which theamounts of tin, nitrogen, and niobium are mainly controlled, and whichcomprises 0˜1.5 wt % of tin, 0˜0.24 wt % of iron, 0˜0.15 wt % ofchromium, 0˜2300 ppm of nitrogen, 0˜100 ppm of silicon, 0˜1600 ppm ofoxygen, and 0˜0.5 wt % of niobium.

U.S. Pat. No. 5,211,774 discloses a zirconium alloy composition in orderto increase the mechanical properties and corrosion properties in aneutron irradiation environment. The alloy is composed of 0.8˜1.2 wt %of tin, 0.2˜0.5 wt % of iron, 0.1˜0.4 wt % of chromium, 0˜0.6 wt % ofniobium, 50˜200 ppm of silicon, and 900˜1800 ppm of oxygen, in which theamount of silicon is varied in order to decrease changes in hydrogenabsorption and corrosion resistance.

In the conventional techniques related to the zirconium alloys mentionedabove, Zircaloy-4 and various zirconium alloys have been mainlydeveloped, and furthermore, the zirconium alloys containing niobium,iron, and chromium have also been developed in order to increasecorrosion resistance. However, compared to such zirconium alloys, thedevelopment of zirconium alloys, having superior corrosion resistancesuitable for high burn-up and extended fuel cycle operating conditionsin nuclear power plants, is still required.

SUMMARY OF THE INVENTION

Leading to the present invention, thorough research into zirconiumalloys having high corrosion resistance, carried out by the presentinventors aiming to solve the problems encountered in the prior art,resulted in the development of a zirconium alloy composition havingexcellent corrosion resistance by controlling the amounts of alloyingelements, including niobium, iron, copper, silicon, carbon, and oxygen.

An object of the present invention is to provide a zirconium alloycomposition having excellent corrosion resistance, which can be used asmaterial for nuclear fuel cladding tubes and core components under hightemperature/high pressure conditions of light water reactors and heavywater reactors.

In order to accomplish the above object, the present invention providesa zirconium alloy composition having excellent corrosion resistance,comprising 1.3˜2.0 wt % of niobium, 0.05˜0.18 wt % of iron, 0.008˜0.012wt % of silicon, and 0.1˜0.16 wt % of oxygen, with the balance beingzirconium.

In addition, the present invention provides a zirconium alloycomposition having excellent corrosion resistance, comprising 2.8˜3.5 wt% of niobium, 0.2˜0.7 wt % of at least one of iron and copper,0.008˜0.012 wt % of silicon, 0.008˜0.012 wt % of carbon, and 0.1˜0.16 wt% of oxygen, with the balance being zirconium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the corrosion properties of the zirconiumalloy with respect to water (O) and steam (□) depending on the amount ofiron in the Zr—1.5Nb—xFe—0.01Si-0.01C—0.13O alloy; and

FIG. 2 is a graph showing the corrosion properties of the zirconiumalloy with respect to water (O) and steam (□) depending on the totalamount of iron and copper in the Zr—3.0Nb—x(Fe+Cu)—0.01Si—0.01C—0.13Oalloy.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a detailed description will be given of the presentinvention.

According to the present invention, the zirconium alloy compositioncomprises 1.3˜2.0 wt % of niobium, 0.05˜0.18 wt % of iron, 0.008˜0.012wt % of silicon, and 0.1˜0.16 wt % of oxygen, with the balance beingzirconium, and preferably comprises 1.4˜1.6 wt % of niobium, 0.08˜0.12wt % of iron, 0.009˜0.011 wt % of silicon, 0.009˜0.011 wt % of carbon,and 0.12˜0.14 wt % of oxygen, with the balance being zirconium.

In addition, the zirconium alloy composition according to the presentinvention comprises 2.8˜3.5 wt % of niobium, 0.2˜0.7 wt % of at leastone of iron and copper, 0.008˜0.012 wt % of silicon, 0.008˜0.012 wt % ofcarbon, and 0.1˜0.16 wt % of oxygen, with the balance being zirconium,and preferably comprises 2.8˜3.2 wt % of niobium, 0.4˜0.6 wt % of atleast one of iron and copper, 0.009˜0.011 wt % of silicon, 0.009˜0.011wt % of carbon, and 0.12˜0.14 wt % of oxygen, with the balance beingzirconium.

The most important problem to be solved for nuclear fuel used in highburn-up and extended cycle conditions is the drastic increase in surfacecorrosion due to high heat flux and long exposure time under reactorconditions. When the corrosion is increased, an oxide film, which ishighly brittle, is increasingly formed, and furthermore, hydrogen isintroduced in a large amount into a matrix, undesirably deterioratingthe structural soundness of nuclear fuel rods. Thus, the development ofmaterial for cladding tubes having excellent corrosion resistance candirectly contribute to the increase in economic efficiency of lightwater reactors and heavy water reactors and the improvement of safetythereof. In the present invention, with the goal of inhibiting thecorrosion under reactor conditions, niobium, which is known to greatlycontribute to an increase in corrosion resistance in a neutronirradiation environment, is added in as large an amount as possible.Further, iron and copper are added in appropriate amounts, thusincreasing corrosion resistance.

Below, individual elements of the zirconium alloy composition of thepresent invention are specifically described.

(1) Niobium (1^(st) Alloying Element)

Niobium is known as a β-phase stabilizer element of zirconium. Theinfluence of niobium on corrosion resistance is variable. Typically,when niobium is added in an amount of 0.5 wt % or less (low niobiumcontent) or 1.0 wt % or more (high niobium content), corrosionresistance is known to be improved.

When niobium is added to a zirconium matrix in an amount not less than asolid solubility thereof, the zirconium matrix is hardened due to thesolid solution of niobium and precipitation of niobium, thus improvingthe mechanical properties of zirconium.

The niobium, which is added to the zirconium alloy, essentiallyfunctions to increase corrosion resistance and also affects an increaseof tensile and creep performance. The amount of niobium used in thepresent invention may be adjusted depending on the amount of at leastone of iron and copper. In the case where iron, acting as a secondalloying element, is used in an amount less than 0.2 wt %, niobium ispreferably added in an amount of 1.3˜2.0 wt %. On the other hand, in thecase where at least one of iron and copper is added in an amount notless than 0.2 wt %, niobium is preferably added in an amount of 2.8˜3.5wt %. If the amount thereof falls outside of the above range, thecorrosion resistance of the zirconium alloy is decreased.

(2) Iron and Copper (2^(nd) Alloying Elements)

Iron and copper, which are added as second alloying elements, are knownto increase the corrosion resistance of the zirconium alloy. Even whenthey are added in very small amounts, corrosion resistance is increased.In the zirconium alloy composition according to the present invention,when iron is added in an amount less than 0.2 wt %, the amount thereofis preferably controlled in the range of 0.05˜0.18 wt %. On the otherhand, in the case where iron and copper is added in an amount not lessthan 0.2 wt %, the amount thereof is preferably adjusted in the range of0.2˜0.7 wt %. If the amount thereof falls outside of the above range,the corrosion resistance of the zirconium alloy is decreased.

In the zirconium alloy composition of the present invention, the amountof niobium is increased in proportion to an increase in amount of atleast one of iron and copper. However, when the total amount of iron andcopper added exceeds 0.7 wt %, defects in the working zone may occur.Consequently, it is preferred that the total amount of iron and copperbe not more than 0.7 wt %.

(3) Silicon, Carbon, and Oxygen

Silicon and carbon function to decrease hydrogen absorption in thezirconium matrix and to retard a transition phenomenon, causing adrastic increase in corrosion over time, and oxygen is dissolved in thezirconium matrix to generate a solid solution so as to increase themechanical strength of the zirconium alloy.

In the zirconium alloy composition of the present invention, silicon andcarbon, which are used in a very small amount, are preferably added inan amount of 0.008˜0.012 wt %, and oxygen is preferably added in anamount of 0.1˜0.16 wt %. If the amount of silicon and carbon fallsoutside of the above range, corrosion resistance is decreased, andfurthermore, if the amount of oxygen falls outside of the above range,low corrosion resistance and poor workability may result.

The zirconium alloy composition of the present invention may be preparedusing a typical process known in the art, and the preparation methodthereof preferably comprises a first step of mixing and melting alloyingelements to thus prepare an ingot, a second step of heat treating theingot prepared in the first step in a β-region and cooling it, a thirdstep of subjecting the ingot heat treated and cooled in the second stepto hot rolling, and a fourth step of subjecting the ingot treated in thethird step to cold rolling and heat treating, thus preparing a zirconiumalloy. After the cold rolling of the fourth step, final heat treatmentmay be further included.

Below, the preparation method of the present invention is stepwiselydescribed in detail.

The first step is a process of mixing the alloying elements at apredetermined ratio and melting them, thus preparing the ingot.

The ingot is preferably prepared using a vacuum arc remelting (VAR)process. Specifically, the vacuum state in a chamber is maintained at1×10⁻⁵ torr, after which argon (Ar) gas is injected thereto at 0.1˜0.3torr and 500˜1000 A of current is applied, to thus perform the meltingprocess, and then a cooling process is conducted, thereby preparing theingot in the shape of a button.

As such, in order to prevent the segregation of impurities or thenon-uniform distribution of the alloy composition in the button, it ispreferred that the melting process be repeated three to six times. Inthe cooling process, in order to prevent the surface of the test piecefrom being oxidized, inert gas, such as argon, is preferably injected.

Subsequently, the second step is a process of heat treating the ingot,prepared in the first step, in a β-region and then cooling it.

To homogenize the alloy composition in the ingot and obtain fineprecipitates, the ingot is heat treated in a β-region and then cooled.As such, with the goal of preventing the test piece from being oxidized,the test piece is clad with stainless steel, and heated treated at1000˜1200° C., and preferably at 1020˜1070° C., for 5-30 min, andpreferably for 10-20 min. After the heat treatment, a quenching processusing water at room temperature is preferably performed.

Subsequently, the third step is a process of hot rolling the test piecetreated in the second step. Specifically, the hot rolling process isperformed in a manner such that the test piece is preheated to 550˜750°C., and preferably to 580˜610° C., for 2˜50 min, and preferably for 5˜40min, and is rolled at a reduction ratio of 40˜80%, and preferably50˜70%.

After the hot rolling process is performed, the cladding is removed, andthen an oxide film which is generated upon β-heat treatment or hotrolling, is removed using an acid solution. Furthermore, portions of theoxide film, remaining after the acid cleaning process, may be completelyremoved through a mechanical process using an electromotive wire brush.

Subsequently, the fourth step is a process of cold rolling and heattreating the test piece which was hot rolled in the third step, thuspreparing the zirconium alloy.

The hot rolled test piece is subjected to annealing at 550˜610° C., andpreferably at 560˜600° C., for a time period from 20 min to 3 hours, andthen to cold rolling at a reduction ratio of 40˜60%, after which heattreatment at 560˜600° C. for 1˜3 hours and cold rolling are repeated. Inthis case, the heat treatment and cold rolling are repeated severaltimes, and preferably, three to five times.

After the final cold rolling process is performed, final heat treatmentfor recrystallization or relieving residual stress may be furtherincluded. This final heat treatment is preferably performed at 500˜600°C. for 1˜3 hours. According to this method, the zirconium alloycomposition according to the present invention can be prepared.

As the results of a corrosion test, the zirconium alloy composition ofthe present invention, comprising the above elements and amounts, can beseen to exhibit excellent corrosion resistance (Table 2), and thereforecan be usefully used in high burn-up nuclear fuel cladding tubes,support ribs, and structural components of nuclear power plants.

A better understanding of the present invention may be obtained throughthe following examples, which are set forth to illustrate, but are notto be construed as the limit of the present invention.

EXAMPLE 1 Preparation of Zirconium Alloy

(1) Preparation of Ingot

A zirconium alloy composition, comprising 1.58 wt % of niobium, 0.05 wt% of iron, 0.01 wt % of silicon, 0.01 wt % of carbon, and 0.13 wt % ofoxygen, with the balance being zirconium, was subjected to VAR to thusprepare an ingot having a weight of 200 g in a button shape. As such, aszirconium, reactor grade sponge zirconium, described in ASTM B349, wasused, and the alloying elements had high purity of 99.99% or more. Inaddition, silicon, carbon, and oxygen were subjected along with spongezirconium to first melting to thus prepare a mother alloy, which wasthen added in a desired amount upon ingot melting. In order to preventthe segregation of impurities or the non-uniform distribution of thealloy composition, the melting process was repeated four times. Further,in order to prevent the oxidation upon the melting process, the vacuumstate in a chamber was maintained at 1×10⁻⁵ torr, argon gas having highpurity of 99.99% was injected, and 500 A of current was applied, andthus an ingot was prepared in a water-cooled copper crucible having adiameter of 60 mm at a water pressure of 1 kgf/cm².

(2) β-Heat Treatment

To uniformly distribute the alloy composition in the ingot, the preparedingot was subjected to solution heat treatment at 1050° C., which was aβ-phase temperature, for 15 min. To prevent the test piece from beingoxidized, the test piece was clad with a stainless steel plate 1 mmthick. After the completion of the heat treatment, the ingot was droppedinto a water bath filled with water at room temperature to thus bequenched, resulting in a martensite structure. Thereafter, the ingot wasdried at 150° C. for 24 hours to remove water from the cladding thereof.

(3) Hot Rolling

A hot rolling process was performed using a rolling mill having acapacity of 100 tons. The test piece was preheated to 590° C. for 30 minand then rolled at a reduction ratio of about 70% per pass. After thehot rolling process, the cladding was removed, and an oxide film,resulting from β-heat treatment or hot rolling, was removed using anacid solution comprising hydrofluoric acid:nitric acid:water=5%:45%:50%at a volume ratio. Subsequently, portions of the oxide film remainingafter the acid cleaning were completely removed using an electromotivewire brush.

(4) Cold Rolling and Heat Treatment

In order to remove residual stress after the hot rolling process and toprevent the test piece from breaking down when first cold rolled, thetest piece was annealed at 590° C. for 30 min, and was then subjected tofirst cold rolling at a reduction ratio of 50% according to a decreasein thickness of about 0.5 mm per pass using a rolling mill having acapacity of 70 tons. Thereafter, the first cold rolled test piece wassubjected to intermediate recrystallization heat treatment at 570° C.for 2.5 hours, and then to second cold rolling at a reduction ratio of50%. Thereafter, the second cold rolled test piece was subjected tointermediate recrystallization heat treatment at 570° C. for 2.5 hoursand then to third cold rolling at a reduction ratio of 50%.

(5) Final Heat Treatment

The test piece was subjected to final heat treatment at 510° C. for 2.5hours to relieve the stress generated after the cold rolling process.The test piece, which was subjected to final heat treatment, was about0.7 mm thick.

EXAMPLE 2

The present example was performed in the same manner as in Example 1,with the exception that a zirconium alloy composition, comprising 1.51wt % of niobium, 0.09 wt % of iron, 0.01 wt % of silicon, 0.01 wt % ofcarbon, and 0.13 wt % of oxygen, with the balance being zirconium, wasused.

EXAMPLE 3

The present example was performed in the same manner as in Example 1,with the exception that a zirconium alloy composition, comprising 1.72wt % of niobium, 0.14 wt % of iron, 0.01 wt % of silicon, 0.01 wt % ofcarbon, and 0.13 wt % of oxygen, with the balance being zirconium, wasused.

EXAMPLE 4

The present example was performed in the same manner as in Example 1,with the exception that a zirconium alloy composition, comprising 1.38wt % of niobium, 0.18 wt % of iron, 0.01 wt % of silicon, 0.01 wt % ofcarbon, and 0.13 wt % of oxygen, with the balance being zirconium, wasused.

EXAMPLE 5

The present example was performed in the same manner as in Example 1,with the exception that a zirconium alloy composition, comprising 3.01wt % of niobium, 0.21 wt % of iron, 0.01 wt % of silicon, 0.01 wt % ofcarbon, and 0.13 wt % of oxygen, with the balance being zirconium, wasused, and final heat treatment was conducted at 570° C.

EXAMPLE 6

The present example was performed in the same manner as in Example 5,with the exception that a zirconium alloy composition, comprising 3.12wt % of niobium, 0.48 wt % of iron, 0.01 wt % of silicon, 0.01 wt % ofcarbon, and 0.13 wt % of oxygen, with the balance being zirconium, wasused.

EXAMPLE 7

The present example was performed in the same manner as in Example 5,with the exception that a zirconium alloy composition, comprising 3.05wt % of niobium, 0.24 wt % of copper, 0.01 wt % of silicon, 0.01 wt % ofcarbon, and 0.13 wt % of oxygen, with the balance being zirconium, wasused.

EXAMPLE 8

The present example was performed in the same manner as in Example 5,with the exception that a zirconium alloy composition, comprising 2.95wt % of niobium, 0.51 wt % of copper, 0.01 wt % of silicon, 0.01 wt % ofcarbon, and 0.13 wt % of oxygen, with the balance being zirconium, wasused.

EXAMPLE 9

The present example was performed in the same manner as in Example 5,with the exception that a zirconium alloy composition, comprising 3.09wt % of niobium, 0.05 wt % of iron, 0.25 wt % of copper, 0.01 wt % ofsilicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the balancebeing zirconium, was used.

EXAMPLE 10

The present example was performed in the same manner as in Example 5,with the exception that a zirconium alloy composition, comprising 3.11wt % of niobium, 0.27 wt % of iron, 0.28 wt % of copper, 0.01 wt % ofsilicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the balancebeing zirconium, was used.

EXAMPLE 11

The present example was performed in the same manner as in Example 5,with the exception that a zirconium alloy composition, comprising 2.98wt % of niobium, 0.32 wt % of iron, 0.35 wt % of copper, 0.01 wt % ofsilicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the balancebeing zirconium, was used.

COMPARATIVE EXAMPLE 1

The present example was performed in the same manner as in Example 1,with the exception that a zirconium alloy composition, comprising 1.55wt % of niobium, 0.01 wt % of silicon, 0.01 wt % of carbon, and 0.13 wt% of oxygen, with the balance being zirconium, was used without theaddition of copper or iron.

COMPARATIVE EXAMPLE 2

The present example was performed in the same manner as in Example 1,with the exception that a zirconium alloy composition, comprising 3.1 wt% of niobium, 0.01 wt % of silicon, 0.01 wt % of carbon, and 0.13 wt %of oxygen, with the balance being zirconium, was used without theaddition of copper or iron.

COMPARATIVE EXAMPLE 3

A reactor grade Zircaloy-4, which was commercially available as materialfor nuclear fuel cladding tubes of nuclear power plants, was used.

The zirconium alloy compositions are shown in Table 1 below.

TABLE 1 Ratio of Zirconium Alloy Composition No. Nb(wt %) Fe(wt %) Cu(wt%) C(wt %) O(wt %) Si(wt %) Zr Ex. 1 1.58 0.05 0.01 0.13 0.01 BalanceEx. 2 1.51 0.09 0.01 0.13 0.01 Balance Ex. 3 1.72 0.14 0.01 0.13 0.01Balance Ex. 4 1.38 0.18 0.01 0.13 0.01 Balance Ex. 5 3.01 0.21 0.01 0.130.01 Balance Ex. 6 3.12 0.48 0.01 0.13 0.01 Balance Ex. 7 3.05 0.24 0.010.13 0.01 Balance Ex. 8 2.95 0.51 0.01 0.13 0.01 Balance Ex. 9 3.09 0.050.25 0.01 0.13 0.01 Balance Ex. 10 3.11 0.27 0.28 0.01 0.13 0.01 BalanceEx. 11 2.98 0.32 0.35 0.01 0.13 0.01 Balance C. Ex. 1 1.55 0.01 0.130.01 Balance C. Ex. 2 3.10 0.01 0.13 0.01 Balance C. Ex. 3 Sn: 1.35 wt%, Fe: 0.2 wt %, Cr: 0.1 wt %, O: 0.12 wt %, (Zircaloy- Zr: balance 4)

EXPERIMENTAL EXAMPLE 1 Corrosion Test

In order to evaluate the corrosion resistance of the zirconium alloycomposition according to the present invention, the following corrosiontest was conducted.

Each of the zirconium alloys of Examples 1˜11 and Comparative Examples1˜3 was formed into a corrosion test piece in the shape of a couponhaving a size of 15 mm×25 mm×0.7 mm, after which the surface thereof waspolished using SiC polishing paper of 800 grit. Thereafter, the testpiece was dipped into a solution of water:nitric acid:hydrofluoric acidat a volume ratio of 50:45:5, to thus remove impurities and fine defectsfrom the surface thereof. The alloy test piece thus surface treated wasmeasured for surface area and initial weight immediately before it wasloaded into an autoclave. Thereafter, the test piece was loaded into theautoclave, having water at 360° C. (18.5 MPa) and a steam atmosphere at400° C. (10.3 MPa) to thus undergo corrosion for 546 days, after whichthe weight of the test piece was measured. The extent of corrosion wascalculated using the weight increase per surface area, and thusqualitatively evaluated. The results of the corrosion test are shown inTable 2 below.

TABLE 2 Weight Increase (mg/dm²) No. Water at 360° C. Steam at 400° C.Ex. 1 64 198 Ex. 2 56 187 Ex. 3 52 165 Ex. 4 51 159 Ex. 5 68 209 Ex. 661 192 Ex. 7 67 193 Ex. 8 65 178 Ex. 9 63 196 Ex. 10 61 198 Ex. 11 58202 C. Ex. 1 73 223 C. Ex. 2 77 251 C. Ex. 3 172 252

As is apparent from Table 2, in the zirconium alloys of Examples 1˜11comprising the zirconium alloy composition of the present invention, theweight increases attributable to corrosion by water were determined tobe 51˜65 mg/dm², which were lower than those of the comparative examples(73, 77 or 172 mg/dm²), resulting in superior corrosion resistance.Furthermore, even in the case of corrosion by steam, the weightincreases were determined to be 159-209 mg/dm², which were lower thanthose of the comparative examples (223, 251 or 252 mg/dm²), leading toexcellent corrosion resistance. Accordingly, the zirconium alloycomposition of the invention has excellent corrosion resistance withrespect to water and steam, and therefore can be usefully used in highburn-up nuclear fuel cladding tubes, support ribs, and reactorstructural components of nuclear power plants.

EXPERIMENTAL EXAMPLE 2 Corrosion Test Depending on Amount of Iron orCopper

The zirconium alloy of the invention was subjected to the following testto evaluate the corrosion resistance thereof depending on the amount ofiron or copper.

(1) Corrosion Resistance Depending on Amount of Iron

While the amount of iron was increased in the alloy compositions ofExamples 1˜4 and Comparative Example 1 (Zr—1.5Nb—xFe—0.01Si—0.01C—0.13Oalloy), corrosion resistance was qualitatively evaluated in the samemanner as in Test Example 1. The results are shown in FIG. 1.

As illustrated in FIG. 1, as the amount of iron was increased in thezirconium alloy, the weight increase of the test piece was seen to bedecreased. That the weight increase was decreased indicated lessadsorption of impurities, thus resulting in low corrosion. Therefore,when the amount of iron was increased in the zirconium alloy, corrosionresistance was observed to increase.

(2) Corrosion Resistance Depending on Total Amounts of Iron and Copper

While the total amounts of iron and copper (Fe+Cu) was increased in thealloy compositions of Examples 5˜11 and Comparative Example 2(Zr—3.0Nb—x(Fe+Cu)—0.01Si—0.01C—0.13O alloy), corrosion resistance wasqualitatively evaluated using the same manner as in Test Example 1. Theresults are shown in FIG. 2.

As illustrated in FIG. 2, as the total amounts of iron and copper wereincreased in the zirconium alloy, the weight increase of the test piecewas decreased, leading to high corrosion resistance.

As described hereinbefore, the present invention provides a zirconiumalloy composition having excellent corrosion resistance for nuclearapplications and a method of preparing the same. In the zirconium alloycomposition according to the invention, the amount of niobium, acting asa first alloying element, and the amount of at least one of iron andcopper, acting as a second alloying element, are appropriatelycontrolled, and silicon, carbon and oxygen are added in appropriateamounts, therefore realizing excellent corrosion resistance. Thus, thezirconium alloy composition of the invention can be usefully used asmaterials for nuclear fuel cladding tubes, support ribs, and corecomponents of light water reactors and heavy water reactors.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A zirconium alloy composition having excellent corrosion resistancefor nuclear applications, comprising 1.3˜2.0 wt % of niobium, 0.05˜0.18wt % of iron, 0.008˜0.012 wt % of silicon, 0.008˜0.012 wt % of carbon,and 0.1˜0.16 wt % of oxygen, with a balance being zirconium.
 2. Thezirconium alloy composition according to claim 1, wherein saidcomposition comprises 1.4˜1.6 wt % of niobium, 0.08˜0.12 wt % of iron,0.009˜0.011 wt % of silicon, 0.009˜0.011 wt % of carbon, and 0.12˜0.14wt % of oxygen, with the balance being zirconium.
 3. A zirconium alloycomposition having excellent corrosion resistance for nuclearapplications, comprising 2.8˜3.5 wt % of niobium, 0.2˜0.7 wt % of atleast one of iron and copper, 0.008˜0.012 wt % of silicon, 0.008˜0.012wt % of carbon, and 0.1˜0.16 wt % of oxygen, with a balance beingzirconium.
 4. The zirconium alloy composition according to claim 3,wherein said composition comprises 2.8˜3.2 wt % of niobium, 0.4˜0.6 wt %of at least one of iron and copper, 0.009˜0.011 wt % of silicon,0.009˜0.011 wt % of carbon, and 0.12˜0.14 wt % of oxygen, with thebalance being zirconium.
 5. The zirconium alloy composition according toclaim 3, wherein a total amount of the iron and copper is 0.7 wt % orless.
 6. A method of preparing a zirconium alloy composition accordingto claim 1 to 5 comprising: a first step of mixing alloying elements andthen melting them, to thus prepare an ingot; a second step of heattreating the ingot prepared in the first step in a β-region and thencooling it; a third step of hot rolling the ingot heat treated andcooled in the second step; and a fourth step of cold rolling and heattreating the ingot hot rolled in the third step, thus preparing azirconium alloy.
 7. The method according to claim 6, which furthercomprises a final heat treating following a further cold rolling afterthe heat treating in the fourth step.